Fuel control device for cylinder injection type internal combustion engine

ABSTRACT

A fuel control device for cylinder injection type internal combustion engines which is capable of cutting off fuel supplying to a combustion chamber depending upon an operating state of the engine and suitable for use in cylinder injection type engines, in which a compression stroke mode can be selected for the purpose of enabling shifting to fuel cutoff and shifting to fuel injection from cutoff without incurring shock of switching in the engine.

This application is the national phase under 35 U.S.C. §371 of prior PCTInternational Application No. PCT/JP97/02781, which has an Internationalfiling date of Aug. 8, 1997, which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a fuel control apparatus for anin-cylinder injection internal combustion engine suitable for use within-cylinder injection internal combustion engines which can selectaccording to the operating state of the engine a fuel cut mode in whichsupply of fuel to the combustion chamber is cut.

BACKGROUND ART

In spark ignition type internal combustion engines (hereinafter alsoreferred to as engines), including automobile engines, a technique whichattempts to save fuel consumption and also prevent the excessivetemperature rise of an exhaust gas purifying catalyzer due to excesshydrocarbon (HC) by cutting fuel injection from the fuel injection valveto cut supply of fuel to the combustion chamber has recently beendeveloped.

Such a technique is also called fuel cut control. This fuel cut controlcan be performed only under certain conditions, because inevitably itcauses a sudden reduction in the engine output (or, specifically anincrease in the engine brake). In other words, in the case of low enginespeeds, the fuel cut control cannot be carried out because there is thepossibility that engine stall will take place. Of course, similarly,where a driver does not desire deceleration, the fuel cut control cannotbe carried out.

Hence, in the case where the throttle valve is fully closed when theengine speed is greater than a predetermined speed, generally the fuelcut control is attempted to be performed.

In this case, for conditions for the opening degree of the throttlevalve, in addition to a technique for directly detecting and judging athrottle opening degree, there is a technique for judging based onwhether or not an engine is in an idle state.

In other words, the case where an engine goes to an idle state is onewhere the throttle valve is less than a predetermined micro openingdegree, and generally, idle control is performed based on informationfrom an idle switch which operates according to the throttle openingdegree. If the throttle valve is less than a predetermined micro openingdegree, it means this case nearly coincides with the case where thethrottle valve is fully closed. Hence, the technique that causes fuelcut control to be carried out in the case where an engine goes to anidle state when the engine speed is greater than a predetermined speedhas been developed.

However, where fuel cut control is carried out based on whether or notan engine is in an idle state, the fuel cut control is prohibited for apredetermined period after the engine has made a transition from anon-idle state to an idle state, for the purpose of confirming that thethrottle valve has been fully closed.

Also, if fuel cut is performed, a sudden reduction in the output torqueof an engine will be caused. In automobile engines, since a vehicle willbe considerably shocked, another technique has been developed. Even ifthe accelerator pedal is off, the throttle valve will not be fullyclosed suddenly but will be gently closed by operation of a so-calleddashpot, thereby avoiding a sudden reduction in the engine output torqueand a great shock to a vehicle.

The aforementioned fuel cut control, incidentally, has been applied to amultipoint injection (MPI) engine equipped with fuel injection valveseach in an intake port of each cylinder, but, since an in-cylinderinjection engine (in-cylinder injection internal combustion engine) witha fuel injection valve faced so as to inject fuel directly into thecombustion chamber within the cylinder has been developed in recentyears, the fuel cut control is desired to be applied to such anin-cylinder injection engine.

Such an in-cylinder injection engine can inject fuel into the combustionchamber at any time regardless of the opening and closing of the intakevalve and therefore can carry out various characteristic operations asfollows:

For example, a fuel injection mode with a compression stroke as primary(this is referred to as a compression stroke injection mode) can be set.In this compression stroke injection mode, stable combustion can berealized in a ultra-lean air-fuel ratio state by stratified combustionmaking use of the stratified intake-air flow formed within the cylinder.In other words, since injected fuel can be collected near the spark plugby making use of stratified intake-air flow, operation can be performedsaving fuel consumption considerably with the entire fuel-air ratiocaused to be in an extremely lean air-fuel state, obtaining stableignitability with only the vicinity of the spark plug caused to be in agood ignitable air-fuel state (i.e., stoichiometric air-fuel ratio stateor air-fuel ratio state on a side slightly richer than thestoichiometric air-fuel ratio state).

Of course, a fuel injection mode with an intake stroke as primary (thisis referred to as an intake stroke injection mode) can be set. In thisintake stroke injection mode, stable ignition and reliable flamepropagation are realized evening the entire air-fuel ratio state of thecombustion chamber by premixing fuel, whereby operation can be performedso that sufficiently high output is obtainable. In this intake strokeinjection mode, a stoichiometric mode in which great output is obtainedby adjusting an air-fuel ratio to near a stoichiometric air-fuel ratioand a lean mode in which fuel consumption can be saved by causing anair-fuel ratio to be leaner than a stoichiometric air-fuel ratio areconsidered. In addition, in view of the case where great output isdesired to be obtained temporarily during rapid acceleration, etc., anenrich mode in which an air-fuel ratio is richer than a stoichiometricair-fuel ratio is considered.

In such an in-cylinder injection engine, incidentally, the engine isoperated by properly selecting various operating modes such as theaforementioned compression stroke injection mode (lean compression modeor late lean mode), a stoichiometric intake stroke injection mode(stoichiometric mode), a lean intake stroke injection mode (lean intakemode or early lean mode), and an enrich intake stroke injection mode(enrich mode). The selection of these operating modes is considered tobe performed based on engine speed and engine load.

In other words, the lean compression mode is selected in an area whereengine speed is low and engine load is small, and if the engine speedbecomes higher than the low engine speed and the engine load becomesgreat, the lean intake mode, the stoichiometric mode, and the enrichmode will be selected in the recited order, as the degree becomesgreater.

Engine load nearly corresponds to the degree of depression of theaccelerator pedal, so when the lean compression mode is selected, thedepression degree of the accelerator pedal is slight and therefore thethrottle opening degree is slight. On the other hand, in the leancompression mode in which operation is performed in a super-lean statein which an air-fuel ratio is extremely great, if there is no sufficientintake-air quantity, the engine output at the same throttle openingdegree will become small. Also, stratified flow will become weak andstable combustion will be difficult to be carried out. Therefore, if athrottle opening degree is slight and an intake-air quantity isregulated with the throttle valve, the operation in the lean compressionmode will be difficult. For this reason, in the in-cylinder injectionengine, the air quantity regulated with the throttle valve issupplemented, by providing a bypass passage (air bypass passage) whichbypasses the throttle valve and controlling the opening degree of avalve (air bypass valve) provided in the air bypass passage.

However, if such fuel cut control employed in the conventional MPIengine, as it is, is applied to such an in-cylinder injection engine, asudden reduction in the output torque of the engine will be caused whenfuel cut is started, and in the case of a vehicle-mounted engine, avehicle will be considerably shocked.

FIG. 9 is a diagram schematically showing the characteristics of theoutput torque of an engine in the case where the engine makes atransition from a non-idle state to an idle state when the engine speedis greater than a predetermined speed (fuel cut condition speed) Ne1 andthen makes a transition to a fuel cut mode. In the figure, "A"represents a torque change characteristic in the case of theconventional MPI engine and "B" represents a torque changecharacteristic in the case of the in-cylinder injection engine. In thiscase, after establishment of fuel cut conditions (i.e., after the enginehas gone to an idle state), the throttle valve is not fully closedsuddenly but is gently closed through operation of a so-called dashpot.

As shown in FIG. 9, in the conventional MPI engine, in the circumstancesin which fuel cut control is started, i.e., in the case where thethrottle valve is fully closed or the engine is in an idle state (seeFIG. 9(A)), irregular combustion takes place in the engine and thereforethe engine output torque is already reduced easily. With the operationof the dashpot, the intake-air quantity is reduced, accordingly the fuelinjection quantity is also reduced, and the engine output torque isconsiderably reduced. For this reason, when a transition to a fuel cutmode is made, the torque difference di becomes small as shown in FIG.9(B) and a vehicle will not be easily shocked.

On the other hand, in the in-cylinder injection engine, in thecircumstances in which fuel cut control is started, i.e., in the casewhere the throttle valve is fully closed or the engine is in an idlestate, operation is generally performed in the lean compression mode.However, in this lean compression mode, combustion is favorablyperformed even with a small quantity of fuel injection. Therefore, evenif the engine goes to an idle state and the dashpot is operated, theengine output torque will be difficult to be reduced. For this reason,when a transition to a fuel cut mode is made, the torque difference d2becomes great as shown in FIG. 9(B), gives a great shock to a vehicle,and easily gives a feeling of physical disorder to the driver, etc.

Such a disadvantage of a vehicle being considerably shocked does notarise only when a transition to a fuel cut mode is made, but it alsoarises when a return from a fuel cut mode to a fuel injection mode ismade.

In other words, even if the engine remains in an idle state, if theengine speed is excessively reduced, in the case where there is arequest to increase engine torque thereafter, the engine cannot quicklycorrespond to the request. Therefore, even in an idle state, if enginespeed is reduced to less than a predetermined speed (fuel injectionreturn condition speed) Ne2 (Ne2<Ne1), a return to a fuel injection modewill be performed.

At this time, torque fluctuation will occur by the amount of the torquedifference d2 such as that shown in FIG. 9. After all, a vehicle willhave a great shock (acceleration shock).

Note that if the engine goes from an idle state to a non-idle stateduring a fuel cut mode, of course the fuel cut mode will return to thefuel injection mode. At this time, a driver depresses the acceleratorpedal to request acceleration, so even if an acceleration shock takesplace, the driver will not easily have a feeling of physical disorderand this case will not be a great problem.

As previously described, such problems are conspicuous in in-cylinderinjection internal engines, but, in a conventional engine (portinjection engine), in order to reduce a torque shock which occurs at thetime of a transition to a fuel cut mode and at the time of a return to afuel injection mode, the techniques that cause a fuel supply quantity tobe reduced gradually at the time of a transition to a fuel cut mode andcause a fuel supply quantity to be increased gradually at the time of areturn Lo a fuel injection mode are disclosed, for example, in JapanesePatent Publication Nos. SHO 58-20374 and SHO 63-42098.

These techniques, however, are for port injection engines, so if thefuel injection quantity at the time of a start of fuel cut and the fuelinjection quantity at the time of a return to fuel cut, disclosed inthese prior techniques, are employed to control fuel cut in thecompression stroke injection mode of an in-cylinder injection engine,there will be the problem that output will be excessive and therefore atorque shock will occur, as previously described. Therefore, thistechnical idea, as it is, cannot be applied to the in-cylinder injectionengine to which the present invention is applied. In other words, thein-cylinder injection engine has a particular fuel injection mode suchas the compression stroke injection mode, as previously described, andfor the torque shock reduction at the time of the switching between thefuel injection mode and the fuel cut mode, a particular efficienttechnique is desired to be developed.

The present invention has been made in view of the aforementionedproblems, and accordingly, it is an object of the invention to provide afuel control apparatus for an in-cylinder injection internal enginewhich can start fuel cut control without causing a switching shock evenin an in-cylinder injection internal engine. Another object of theinvention is to provide a fuel control apparatus for an in-cylinderinjection internal engine which can make a transition to a fuel cut modeand a transition from a fuel cut mode to a fuel injection mode withoutcausing a switching shock, contriving air-fuel ratio control in acompression stroke injection mode in an in-cylinder injection internalengine.

SUMMARY OF THE INVENTION

For those objects, in a fuel control apparatus for an in-cylinderinjection internal combustion engine of the present invention, theinternal combustion engine injects fuel directly into a combustionchamber and is able to select according to an operating state of theinternal combustion engine a compression stroke injection mode in whichfuel injection is performed mainly on a compression stroke. The fuelcontrol apparatus comprises: deceleration state detection means fordetecting whether or not the internal combustion engine is in adeceleration state; idle detection means for detecting whether or notthe internal combustion engine is in an idle state; target air-fuelratio setting means for setting a target air-fuel ratio in thecompression stroke injection mode; and air-fuel ratio control meanswhich can control an air-fuel ratio, based on the target air-fuel ratioset by the target air-fuel ratio setting means; wherein the targetair-fuel ratio setting means sets a first target air-fuel ratio as thetarget air-fuel ratio, when the deceleration state detection meansdetects that the internal combustion engine is in a deceleration stateand also the idle state detection means detects that the internalcombustion engine is not in an idle state, at the time of thecompression stroke injection mode, and also sets as the target air-fuelratio a value changed stepwise toward a second target air-fuel ratio ona leaner side than the first target air-fuel ratio, when thedeceleration state detection means detects that the internal combustionengine is in a deceleration state and also the idle detection meansdetects that the internal combustion engine is in an idle state, at thetime of the compression stroke injection mode.

With this, at the time of the compression stroke injection mode, whenthe internal combustion engine is in a deceleration state but not in anidle state, the first target air-fuel ratio is set as a target air-fuelratio, and when the internal combustion engine is in a decelerationstate and in an idle state, a value changed stepwise toward a secondtarget air-fuel ratio on a leaner side than the first target air-fuelratio is set as a target air-fuel ratio.

Therefore, even if the engine is in a non-idle state duringdeceleration, the engine output torque will be reduced. Thereafter, inthe case where the engine goes to an idle state (generally, in the casewhere fuel cut conditions are established), even when a transition tofuel cut mode is made, the transition can be quickly made without atorque shock.

In addition, when the engine goes to an idle state during deceleration,the target air-fuel ratio for each control cycle is set so that itgradually approaches such a second target air-fuel ratio as to furtherreduce the engine output torque. Therefore, in the case where the enginegoes to an idle state during deceleration and fuel cut conditions areestablished, the engine output torque can be sufficiently reduced and atransition to fuel cut mode thereafter can also be performed without atorque shock.

Thus, the transition to fuel cut mode can be made reducing the outputtorque of the engine, and there is the advantage that fuel cut controlcan be quickly started suppressing a torque shock.

Note that the first target air-fuel ratio preferably is set so as tochange stepwise to a lean side.

Furthermore, in such construction, preferably the target air-fuel ratiosetting means first increases the target air-fuel ratio instantly to athird target air-fuel ratio on a richer side than the second targetair-fuel ratio and then sets a value changed stepwise toward the secondtarget air-fuel ratio, when the deceleration state detection meansdetects that the internal combustion engine is in a deceleration stateand also the idle detection means detects that the internal combustionengine is in an idle state, at the time of the compression strokeinjection mode.

With this, the output torque of the engine can be sufficiently reduced,and the transition to fuel cut mode thereafter can be more quicklyperformed without a torque shock.

In addition, in a fuel control apparatus for an in-cylinder injectioninternal combustion engine of the present invention, the internalcombustion engine injects fuel directly into a combustion chamber and isable to select according to an operating state of the internalcombustion engine a fuel supply mode including a compression strokeinjection mode in which fuel injection is performed mainly on acompression stroke and a fuel cut mode in which supply of fuel to thecombustion chamber is cut. Furthermore, the internal combustion engineis able to select the compression stroke injection mode when it isreturned from the fuel cut mode to the fuel supply mode. The fuelcontrol apparatus comprises: idle detection means for detecting whetheror not the internal combustion engine is in an idle state; judgmentmeans for judging whether or not return conditions from the fuel cutmode to the fuel supply mode have been established, based on detectionformation from the idle detection means and the operating state of theinternal combustion engine; deceleration state detection means fordetecting a degree of deceleration of the internal combustion engine;target air-fuel ratio setting means for setting a target air-fuel ratiofor the compression stroke injection mode; and air-fuel ratio controlmeans which can control an air-fuel ratio, based on the target air-fuelratio set by the target air-fuel ratio setting means; wherein the targetair-fuel ratio setting means sets a first target air-fuel ratio as thetarget air-fuel ratio, when the judgment means judges that the returnconditions have been established and also the degree of decelerationdetected by the deceleration state detection means is equal to orgreater than a predetermined value; also sets as the target air-fuelratio a second target air-fuel ratio on a leaner side than the firsttarget air-fuel ratio, when the judgment means judges that the returnconditions have been established and also the degree of decelerationdetected by the deceleration state detection means is less than thepredetermined value; and furthermore performs a return from the fuel cutmode to the fuel supply mode, while the air-fuel ratio control means iscontrolling an air-fuel ratio with the first or second return targetair-fuel ratio set by the target air-fuel ratio setting means, at thetime of the establishment of the return conditions.

Therefore, when the return conditions are established and also thedegree of deceleration is equal to or greater than a predeterminedvalue, the first target air-fuel ratio is set as a target air-fuelratio, and when the return conditions are established and also thedegree of deceleration is less than the predetermined value, the secondtarget air-fuel ratio on a leaner side than the first target air-fuelratio is set as the target air-fuel ratio. At the time of theestablishment of the return conditions, the return from the fuel cutmode to the fuel supply mode is performed, controlling an air-fuel ratiowith the first or second return target air-fuel ratio.

With this, during the sudden deceleration of the internal combustionengine, if an increase in the engine output torque is insufficient, areduction in the engine speed cannot be prevented, but, if therelatively rich first return target air-fuel ratio is set and theair-fuel ratio is controlled, a reduction in the engine speed can beprevented ensuring an increase in the engine output torque. For thisreason, thereafter preparations can be made quickly and smoothly for thereturn control to the original air-fuel ratio. Also, if the decelerationof the internal combustion engine is gentle, the sudden increase in theengine output torque thereafter will cause a torque shock. Therefore, ifthe relatively lean first return target air-fuel ratio is set and theair-fuel ratio is controlled, the fuel supply can be returned withoutcausing a torque shock. For this reason, thereafter if the return targetair-fuel ratio is gradually reduced toward a target air-fuel ratio on afuel-enriched side, it will become possible to control a fuel-air ratiotoward the original air-fuel ratio quickly and smoothly.

Therefore, there is the advantage that a return can be performedcontrolling the engine output torque properly at the time of the returnto fuel cut to fuel supply and that a fuel supply return can beperformed suppressing a torque shock.

Note that the target air-fuel ratio setting means preferably is set sothat in the case where the second return target air-fuel ratio is set asthe target air-fuel ratio, thereafter the target air-fuel ratio isgradually reduced toward the first return target air-fuel ratio on afuel-enriched side.

Furthermore, in a fuel control apparatus for an in-cylinder injectioninternal combustion engine of the present invention, the internalcombustion engine injects fuel directly into a combustion chamber and isable to select according to an operating state of the internalcombustion engine a fuel supply mode including a compression strokeinjection mode in which fuel injection is performed mainly on acompression stroke and an intake stroke injection mode in which fuelinjection is performed mainly on an intake stroke, and a fuel cut modein which supply of fuel to the combustion chamber is cut. The fuelcontrol apparatus comprises: deceleration state detection means fordetecting whether or not the internal combustion engine is in adeceleration state; idle detection means for detecting whether or notthe internal combustion engine is in an idle state; target air-fuelratio setting means for setting a target air-fuel ratio for thecompression stroke injection mode; and air-fuel ratio control meanswhich can control an air-fuel ratio, based on the target air-fuel ratioset by the target air-fuel ratio setting means; wherein the targetair-fuel ratio setting means sets a first target air-fuel ratio as thetarget air-fuel ratio, when the deceleration state detection meansdetects that the internal combustion engine is in a deceleration stateand also the idle detection means detects that the internal combustionengine is not in an idle state, at the time of the compression strokeinjection mode; and wherein the fuel supply mode is switched from thecompression stroke injection mode to the intake stroke injection mode,when the deceleration state detection means detects that the internalcombustion engine is in a deceleration state and also the idle detectionmeans detects that the internal combustion engine is in an idle state,at the time of the compression stroke injection mode.

With this, at the time of the compression stroke injection mode, whenthe internal combustion engine is in a deceleration state and not in anidle state, the first target air-fuel ratio is set as a target air-fuelratio. At the time of the compression stroke injection mode, when theinternal combustion engine is in a deceleration state and in an idlestate, the fuel supply mode is switched from the compression strokeinjection mode to the intake stroke injection mode.

If the fuel supply mode is thus switched from the compression strokeinjection mode to the intake stroke injection mode, the output torque ofthe engine will easily be reduced because irregular combustion which didnot take place in the compression stroke injection mode takes place inthe engine. Therefore, a torque shock can be reduced when a transitionto a fuel cut mode is made.

Therefore, the transition to fuel cut mode can be made reducing theoutput torque of the engine, and there is the advantage that fuel cutcontrol can be quickly started suppressing a torque shock.

Moreover, in a fuel control apparatus for an in-cylinder injectioninternal combustion engine of the present invention, the internalcombustion engine injects fuel directly into a combustion chamber andhas a fuel cut mode in which supply of fuel to the combustion chamber iscut. Furthermore, the internal combustion engine is able to select thefuel cut mode in accordance with an operating state of the internalcombustion engine. The fuel control apparatus comprises: injectionperiod setting means for setting a fuel injection period for the fuelinjection valve; judgment means for judging whether or not fuel cutconditions have been established, based on the operating state of theinternal combustion engine; and mode selection means for selecting thefuel cut mode, if the judgment means judges that the fuel cut conditionshave been established and also the fuel injection period set by theinjection period setting means is less than a predetermined injectionperiod.

Therefore, if the fuel cut conditions have been established and also theset fuel injection period is less than a predetermined injection period,the fuel cut mode will be selected.

Thus, since the fuel cut control is performed after the fuel injectionperiod has been less than a predetermined injection period, a transitionto a fuel cut mode is made after the torque produced by the engine hasbeen reduced to some degree. Therefore, there is the advantage that thefuel cut control can be started, suppressing a torque shock.

In such construction, the mode selection means preferably is constructedso that it selects the fuel cut mode, if the judgment means judges thatthe fuel cut conditions have been established but a state, in which thefuel injection period set by the injection period setting means is notless than a predetermined injection period, continues only for apredetermined period.

Therefore, the suppression of a torque shock cannot be sufficientlyperformed when a transition to a fuel cut mode is made, but a fuel cuteffect can be obtained with reliability.

Furthermore, the in-cylinder injection internal combustion enginepreferably is provided with a fuel supply mode including a compressionstroke injection mode in which fuel injection is performed mainly on acompression stroke and a fuel supply mode including an intake strokeinjection mode in which fuel injection is performed mainly on an intakestroke, and is constructed so that these fuel injection modes can beswitched in accordance with the operating state of the internalcombustion engine. The predetermined injection period preferably is setseparately for each of the fuel injection modes and the predeterminedinjection period in the compression stroke injection mode is set to ashorter period than the predetermined injection period in the intakestroke injection mode.

If the predetermined injection period is set according to the operatingmode of the engine in this way, a suppression effect of torque shockoccurrence and a fuel cut effect can be balanced with each other.

Note that preferably the fuel cut conditions for selecting the fuel cutmode are that rotation speed of the internal combustion engine is equalto or greater than a predetermined rotation speed and that the internalcombustion engine is in an idle state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the essential construction of a fuelcontrol apparatus for an in-cylinder injection internal combustionengine as a first embodiment of the present invention;

FIG. 2 is a timing chart describing the control of the fuel controlapparatus for an in-cylinder injection internal combustion engine as thefirst embodiment of the present invention, (A) showing whether or notthe engine is in an idle state, (B) showing a target air-fuel ratio, (C)showing an injector pulse width (fuel injection time), (D) showing afuel cut state, and (E) showing engine speed;

FIG. 3 is a flowchart describing the control operation of the fuelcontrol apparatus for an in-cylinder injection internal combustionengine as the first embodiment of the present invention;

FIG. 4 is a diagram showing the essential construction of an in-cylinderinjection internal combustion engine according to the first embodimentof the present invention;

FIG. 5 is a control block diagram of the in-cylinder injection internalcombustion engine according to the first embodiment of the presentinvention;

FIG. 6 is a diagram explaining the operating modes of the in-cylinderinjection internal combustion engine according to the first embodimentof the present invention;

FIG. 7 is a flowchart describing the control operation of the fuelcontrol apparatus for an in-cylinder injection internal combustionengine as the first embodiment of the present invention;

FIG. 8 is a timing chart describing the control of the fuel controlapparatus for an in-cylinder injection internal combustion engine as asecond embodiment of the present invention, (A) showing whether or notthe engine is in an idle state, (B) showing a target air-fuel ratio, (C)showing an injector pulse width (fuel injection time), (D) showing afuel cut state, (E) showing engine speed, and (F) showing an operatingmode (fuel injection mode); and

FIG. 9 is a diagram describing problems to be solved by the presentinvention, (A) showing whether or not the engine is in an idle state and(B) showing the output torque of the engine.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will hereinafter be made of an embodiment of the presentinvention by the drawings.

FIGS. 1 through 7 show a fuel control apparatus for an in-cylinderinjection internal combustion engine as a first embodiment of thepresent invention. Based on these figures, the first embodiment will bedescribed.

First, with respect to the construction of the in-cylinder injectioninternal combustion engine (hereinafter referred to as an in-cylinderinjection engine) according to this embodiment, a description will bemade referring to FIG. 4.

In FIG. 4, 1 is an engine main body, 2 an intake passage, 3 a throttlevalve installation portion, 4 an air cleaner, 5 a bypass passage (secondbypass passage), and 6 a second air bypass valve (#2ABV) which canregulate the quantity of air that flows through the bypass passage 5.The intake passage 2 is constituted by an intake pipe 7, a surge tank 8,and an intake manifold 9, connected in this order from the upstreamside. The bypass passage 5 is provided on the upstream side of the surgetank 8. The bypass valve 6 is driven at a required opening degree with astepper motor, but the opening degree of this bypass valve 6 may also beadjusted with the employment of duty control by an electromagneticvalve.

Furthermore, 12 is one section equipped with an idle speed controlfunction, and consists of a bypass passage (first bypass passage) 13 anda first air bypass valve (#1ABV) 14 which serves as a bypass valve. The#1ABV 14 is driven with a stepper motor (not shown). Also, 15 is athrottle valve, and the first bypass passage 13 and the second bypasspassage 5 connect the respective upstream and downstream ends thereof tothe intake passage 2 so as to bypass the portion of the intake passage 2in which the throttle valve 15 is provided.

Furthermore, the opening and closing controls of the second air bypassvalve 6 and the first air bypass valve 14 are controlled through anelectronic control unit (ECU) 16.

Also, 17 is an exhaust passage and 18 a combustion chamber. The openingsof the intake passage 2 and the exhaust passage 17 to the combustionchamber 18, i.e., an intake port 2A and an exhaust port 17A are providedwith an intake valve 19 and an exhaust valve 20.

Then, 21 is a fuel injection valve (injector). In this engine, thisinjector 21 is arranged so as to inject fuel directly into thecombustion chamber 18.

Furthermore, 22 is a fuel tank, 23A through 23E fuel supply paths, 24 alow-pressure fuel pump, 25 a high-pressure fuel pump, 26 a low-pressureregulator, 27 a high-pressure regulator, and 28 a delivery pipe. Thefuel within the fuel tank 22 is driven with the low-pressure fuel pump24, furthermore is pressurized with the high-pressure fuel pump 25, andis supplied in a predetermined high-pressure state to the injector 21through the fuel supply paths 23A and 23B and the delivery pipe 28. Atthis time, the fuel pressure discharged from the low-pressure fuel pump24 is regulated with the low-pressure regulator 26, and the fuelpressure, which is pressurized with the high-pressure fuel pump 25 andguided to the delivery pipe 28, is regulated with the high-pressureregulator 27.

Also, 29 is an exhaust gas recirculation passage (EGR passage) whichrecirculates the exhaust gas in the exhaust passage 17 of the engine 1into the intake passage 2. 30 is a stepper motor type valve (EGR valve)as exhaust gas quantity adjustment means, which adjusts a recirculationquantity of exhaust gas that is recirculated into the intake passage 2through the EGR passage 29. 31 is a passage for restoring blow-by gas,32 a passage for positively ventilating the crank chamber, 33 a valvefor positively ventilating the crank chamber, 34 a canister, and 35 acatalyzer for purifying exhaust gas (here, catalytic converter rhodium(CCRO)).

Incidentally, as shown in FIG. 4, the ECU 16 performs the opening andclosing controls or opening degree controls of the air bypass valves 6and 14 and, furthermore, performs the controls of the injector 21, sparkwire coils (not shown) for spark plugs, and the EGR valve, and thecombustion pressure control by the high-pressure regulator 27. For thesecontrols, as shown in FIG. 4, an air flow sensor 44, an intake-airtemperature sensor 26, a throttle position sensor (TPS) 37 for detectinga throttle opening degree, an idle switch (idle detection means) 38, anair-con switch (not shown), a speed change position sensor (not shown),a wheel speed sensor (not shown), a power steering wheel switch (notshown) for detecting the operating state of a power steering wheel, astarter switch (not shown), a first-cylinder detection sensor 40, acrank angle sensor 41, a water temperature sensor 42 for detectingtemperature of engine cooling water, an O₂ -sensor 43 for detectingoxygen concentration in exhaust gas, etc., are provided, and connectedto the ECU 16. Note that, based on the crank angle sensor 41, enginespeed can be computed and an engine speed computation function such asthis is provided, for example, in the ECU 16. Hence, in this embodimentthe crank angle sensor 41 is also called an engine speed sensor forconvenience' sake, though the engine speed sensor is constituted by thecrank angle sensor 41 and the engine speed computation function.

Now, the controlled contents regarding the engine through the ECU 16will be described based on a control block diagram of FIG. 5.

This engine is one which switches premixed combustion and stratifiedlean combustion in accordance with the operating state. The premixedcombustion can be established by injecting fuel evenly into thecombustion chamber 18, and the stratified lean combustion can beestablished by causing injected fuel to be unevenly distributed around aspark plug (not shown) facing into the combustion chamber 18.

Then, this engine is provided, as engine operating modes, with a fuelcut mode in which fuel injection is cut, in addition to four fuelinjection modes: late lean combustion operating mode (late lean mode) inwhich fuel is injected on the compression stroke to perform stratifiedlean combustion, early lean combustion operating mode (early lean mode)in which fuel is injected on the intake stroke to perform premixedcombustion, stoichiometric feedback operating mode (stoichiometricmode), and open-loop combustion operating mode (stoichiometric mode orenrich mode).

Then, any of these modes is selected according to the operating state ofthe engine or the traveling state of the vehicle by this fuel controlapparatus for an in-cylinder injection internal combustion engine tocarry out fuel supply control. Note that in each fuel injection mode,the case that the EGR is caused to be operated and the case that the EGRis caused to be stopped are set.

Now, a description will be made of this fuel control apparatus for anin-cylinder injection internal combustion engine. As shown in FIG. 1,the operating states of the engine, i.e., the engine load state Pe andthe engine speed Ne are input from operating-state detection means 101to the ECU 16. The ECU 16 is provided with mode selection means 102 forselecting any of the aforementioned operating modes from the informationof these operating states.

Note that as described later, since the engine load state Pe is computedbased on the engine speed Ne and the throttle opening degree θth, thedata of the engine operating states which are input to the ECU 16 arethe engine speed Ne and the throttle opening degree θth. Theoperating-state detection means 101 comprises an engine speed sensor 41and a throttle opening degree sensor 37.

Also, as shown in FIG. 1, this fuel control apparatus is provided, asthe functional sections within the ECU 16, with target air-fuel ratiosetting means 107 for setting a target air-fuel ratio in accordance witheach operating mode and air-fuel ratio control means 108 for controllingan air-fuel ratio, based on the target air-fuel ratio set by the targetair-fuel ratio setting means 107.

The target air-fuel ratio setting means 107 sets, for example, in thelate lean mode an air-fuel ratio within an air-fuel area where fuel isleanest (greater by far than the stoichiometric air-fuel ratio). In theearly lean mode an air-fuel ratio is set within an air-fuel area wherefuel is leaner than the late lean made (to some degree greater than thestoichiometric air-fuel ratio). In the stoichiometric mode an air-fuelratio is set so as to pulsate with an air-fuel ratio near thestoichiometric air-fuel ratio by the O₂ -feedback control. In the enrichmode an air-fuel ratio is set within an air-fuel ratio area where fuelis rich (slightly less than the stoichiometric air-fuel ratio). Ineither mode other than the stoichiometric mode, a target air-fuel ratiois adjusted according to the operating state of the engine.

The air-fuel ratio control means 108 comprises fuel injection valvecontrol means 105 for controlling the operation of the fuel injectionvalve 21 and intake-air control means 109 for controlling the air bypassvalves (ABV, etc.), and controls an air-fuel ratio by fuel injectionquantity control and intake-air quantity control.

When any of the fuel injection modes is selected, the fuel injectionvalve control means 105 also sets an air-fuel ratio in accordance withthe engine operating states (Pe and Ne) for each of the selectedoperating modes and, based on the set air-fuel ratio, controls theoperation of the fuel injection valve 21 provided in each of thecylinders to control fuel supply. When the fuel cut mode is selected,the fuel injection valve control means 105 cuts fuel which is suppliedby the fuel injection valve 21.

Of course the control of an air-fuel ratio is not carried out by theoperation of the fuel injection valve 21 but it is also carried outalong with the opening and closing controls or opening degree controlsof the air bypass valves 6 and 14. Particularly, at the time of the latelean mode (lean compression mode), air is supplied through the airbypass valve 6 to supplement intake air that becomes insufficient byregulation of the throttle valve, thereby achieving a great air-fuelratio.

Specifically, the fuel injection valve control means 105 sets the driveperiod of the fuel injection valve 21, i.e., the fuel injection period(injector pulse width), and outputs a drive command signal to the fuelinjection valve 21 in accordance with this setting. For this reason, thefuel injection valve control means 105 is provided with injection periodsetting means 106 for setting a fuel injection period. Note that thefuel injection valve control means 105 does not set only a period forinjecting fuel, but it also specifically sets the start timing and endtiming of the fuel injection so that the fuel injection is performed atoptimum timing.

The cases where the mode selection means 102 selects the fuel cut mode,incidentally, are the following cases:

(1) Case where a first predetermined period N1IG elapses after thejudgment means 103 shown in FIG. 1 has judged that fuel cut conditionshave been established and also the fuel injection period set by theinjection period setting means of the fuel injection valve control means105 is less than a predetermined injection period.

(2) Case where the first predetermined period N1IG elapses after thejudgment means 103 shown in FIG. 1 has judged that fuel cut conditionshave been established, but the state, in which the fuel injection periodset by the injection period setting means of the fuel injection valvecontrol means 105 is not less than the predetermined injection period,continues only for a second predetermined period after fuel cutconditions have been established.

Also, the case where the mode selection means 102 selects the engineoperating mode so that it returns from the fuel cut mode to the fuelsupply mode is one where the judgment means 103 shown in FIG. 1 judgesthat release of fuel cut has been established.

Note that, based on detection information from the engine speed sensor41 and the idle switch 38, the judgment means 103 judges that fuel cutconditions have been established, when the engine speed Ne is equal toor greater than a predetermined speed Ne1 and also the idle switch 38outputs an idle command signal corresponding to a nearly fully closedstate of the throttle valve.

Also, the reason why there is a wait for the elapse of the firstpredetermined period N1IG after the judgment means 103 has judged thatfuel cut conditions have been established is for confirming that thethrottle valve has been fully closed, and fuel cut is prohibited duringthe first predetermined period N1IG after the engine has gone from anon-idle state to an idle state. Note that the first predeterminedperiod N1IG is set to a sufficiently short period (8 through 16 IG, forexample).

In other words, if the first predetermined period N1IG elapses after thejudgment means 103 has judged that fuel cut conditions have beenestablished, then the mode selection means 102 will monitor the fuelinjection period set by the injection period setting means 106 andselect the fuel cut mode in the case where this fuel injection period isless than a predetermined injection period α. Also, even if the fuelinjection period is not less than a predetermined injection period αafter the judgment means 103 has judged that fuel cut conditions havebeen established, the mode selection means 102 will select the fuel cutmode if a previously set period (second predetermined period) N2IGelapses. Note that the second predetermined period N2IG is set to aperiod (64 IG, for example) longer than the first predetermined periodN1IG.

That is, even if fuel cut conditions are established and the firstpredetermined period N1IG elapses, fuel cut is not performed until thefuel injection period becomes less than the predetermined injectionperiod α or the second predetermined period N2IG elapses. The reason whythere is a wait until the fuel injection period becomes less than thepredetermined injection period α is that the occurrence of a torqueshock is suppressed when a transition to a fuel cut mode is made, byperforming the fuel cut after the output torque produced by combustionin the engine has become sufficiently small.

Also, the reason that if the second predetermined period N2IG elapses,fuel cut will be performed even if the fuel injection period is not lessthan the predetermined injection period α is that acquisition of a lowfuel consumption effect or an engine brake effect by fuel cut is causedto be prior to suppression of torque shock occurrence. In practice, itis believed that the fuel injection period often becomes less than thepredetermined injection period α before the second predetermined periodN2IG elapses.

The predetermined injection period α, incidentally, is set according tothe engine operating mode (fuel injection mode) by the ECU 16. Thisperiod α is set to a sufficiently small value so that a torque shock canbe suppressed. In the compression stroke injection mode such as the latelean mode, since boost pressure is also low and engine output torque issmall, the fuel injection period will become less than the predeterminedinjection period α quickly (within the second predetermined period N2IG)even if the predetermined injection period α is set relatively small.However, in the intake stroke injection mode such as the early lean modeor the stoichiometric mode, since boost pressure is high and combustionefficiency is not good with respect to the compression stroke injectionmode, the fuel injection period will not be less than the predeterminedinjection period α quickly (within the second predetermined period N2IG)if the predetermined injection period α is set relatively small. Hence,in the case of the intake stroke injection mode, the predeterminedinjection period α is set relatively great so that a suppression effectof torque shock occurrence and a fuel cut effect are balanced with eachother. In the case of the compression stroke injection mode, thepredetermined injection period α is set relatively small so that a fuelcut effect is also obtainable, obtaining a sufficient suppression effectof torque shock occurrence.

Furthermore, in this apparatus, the air-fuel ratio control is performedso that the fuel injection period becomes less than the predeterminedinjection period α quickly and smoothly. In other words, the targetair-fuel ratio setting means 107 sets a target air-fuel ratio inaccordance with each operating mode, but, in the case of the compressionstroke injection mode (i.e., late lean mode), the target air-fuel ratiosetting means 107 will set a target air-fuel ratio during non-idling aswell as during idling so that an air-fuel ratio is gradually increased,if the judgment means 103 judges that the engine is in a decelerationstate.

In other words, from the crank angle sensor 41 as the engine speeddetection means, it can be judged whether or not the engine is in adeceleration state. Therefore, based on information from this crankangle sensor 41 as the engine speed detection means, if the engine is ina deceleration state, the target air-fuel ratio setting means 107 willset a first target air-fuel ratio during non-idling so that an air-fuelratio is gradually increased, and also set a second target air-fuelratio during idling so that the target air-fuel ratio graduallyapproaches the second target air-fuel ratio.

That is, if the engine is in a non-idle state during enginedeceleration, the target air-fuel ratio (first target air-fuel ratio)AF1 will be set so that it is gradually leaned according to thedeceleration state from the air-fuel ratio corresponding to theoperating state, and a target air-fuel for each control cycle will beset to the first target air-fuel ratio AF1 which is gradually leaned inthis way, thereby performing the air-fuel ratio control.

In this manner, even if the engine is in a non-idle state during enginedeceleration, the engine output torque will be reduced, and thereafter,in the case where the engine goes to an idle state (therefore, in thecase where fuel cut conditions are established), a transition to a fuelcut mode can be quickly performed without a torque shock. Of course,since this reduction in the output torque by the increase in theair-fuel ratio is not suddenly performed, there is no possibility thatthe driver, etc., will have a feeling of physical disorder.

Also, if the engine goes to an idle state during engine deceleration,the second target air-fuel ratio (i.e., an air-fuel ratio even higherthan the first target air-fuel ratio) AF2 will be set so that the outputtorque of the engine will be further reduced, and a target air-fuelratio for each control cycle will be set so that it gradually approachesthis second target air-fuel ratio AF2. In this way, in the case wherethe engine goes to an idle state during engine deceleration and alsofuel cut conditions are established, the engine output torque can besufficiently reduced, and the transition to a fuel cut mode thereaftercan be performed without a torque shock. Note that in the intake strokeinjection mode in which a target air-fuel ratio is controlled in thevicinity of the stoichiometric air-fuel ratio, the quantity of fuelinjection which is supplied with the second target air-fuel ratio AF2 isset to a small quantity of fuel injection so that irregular combustionsuch as accidental fire takes place.

Note that in this case, at the time the engine has gone to an idle stateduring engine deceleration, an actual air-fuel ratio must have beenincreased to a third target air-fuel ratio AF2' on a richer side thanthe second target air-fuel ratio AF2, for the reason that decelerationis great and other reasons. First, after an air-fuel ratio has beenincreased instantly to the third target air-fuel ratio AF2', a targetair-fuel ratio for each control cycle is set so that it graduallyapproaches the second target air-fuel ratio AF2 even higher than thethird target air-fuel ratio. The third target air-fuel ratio AF2' needsto be set to a value so that it causes a feeling of deceleration butdoes not cause a shock (feeling of physical disorder), thus byincreasing the air-fuel ratio instantly at the time the engine has goneto an idle state.

If the target air-fuel ratio is set in this manner, the engine outputtorque can be sufficiently reduced, and the transition to a fuel cutmode thereafter can be quickly performed without a torque shock. Inaddition, since such a reduction in the output torque by the increase inthe air-fuel ratio is not suddenly performed, there is no possibilitythat the driver, etc., will have a feeling of physical disorder.

In this apparatus, on the other hand, air-fuel ratio control isperformed at the time of a return from a fuel cut mode to a fuelinjection mode as well. In other words, the mode selection means 102 isset so that it performs a return from a fuel cut mode to a fuel supplymode, if a return condition to a fuel supply mode (fuel injection returnconditions) is established during a fuel cut mode. This fuel injectionreturn condition is the case where a transition from an idle state to anon-idle state is made or the case where engine speed is reduced to lessthan a predetermined speed (fuel injection return condition speed) Ne2(Ne2<Ne1) even if an idle state continues.

This target air-fuel ratio setting means 107 compares the magnitude|ΔNe| of a change rate (actually a reduced speed) ΔNe in the enginespeed Ne with a predetermined value β when this return to a fuel supplymode is performed. If |ΔNe| is less than the predetermined value β(i.e., if a degree of deceleration is slight), a relatively lean secondreturn target air-fuel ratio (less than a stoichiometric air-fuel ratio)B (=AF4) will be set. If |ΔNe| is equal to or greater than thepredetermined value β (i.e., if a degree of deceleration is great), arelative rich first return target air-fuel ratio A (=AF3) will be set.In either case, fuel supply is started with the return target air-fuelratio A or B at the time of a return to a fuel supply mode, but,particularly, in the case where the return target air-fuel ratio B isset, the return target air-fuel ratio thereafter is gradually reducedtoward the target air-fuel ratio A on a fuel-enriched side. Note that inthe intake stroke injection mode in which a target air-fuel ratio iscontrolled in the vicinity of a stoichiometric air-fuel ratio, theinjection quantity of fuel which is supplied with the fourth targetair-fuel ratio AF4 is set so that irregular combustion such as misfiretakes place.

The reasons why different target air-fuel ratios are thus set accordingto the change rate in the engine speed Ne, i.e., the degree ofdeceleration are as follows: When the engine speed Ne is decreasingsuddenly, the speed reduction cannot be prevented if an increase in theengine torque is insufficient. Therefore, the relatively rich targetair-fuel ratio A is set so that the reduction can be avoided, andthereafter, the air-fuel ratio is controlled toward the originalair-fuel ratio quickly and smoothly. If the reduction in the enginespeed Ne is gentle, a sudden increase in the engine torque will cause atorque shock. Therefore, the relatively lean target air-fuel ratio B isset and fuel supply is returned without causing a torque shock.Thereafter, the return target air-fuel ratio is gradually reduced towardthe target air-fuel ratio A on a fuel-enriched side, whereby theair-fuel ratio is controlled toward the original air-fuel ratio quicklyand smoothly.

If the specific examples of such a transition to a fuel cut mode andsuch a return to a fuel supply mode are described, they will become asshown in FIG. 2.

In other words, if the engine goes to a deceleration state during anon-idle state, the target air-fuel ratio AF1 will first be set so thatit is gradually leaned according to the deceleration state from theair-fuel ratio corresponding to the operating state (see FIG. 2(B)), anda target air-fuel ratio for each control cycle will be set to the firsttarget air-fuel ratio AF1 which is thus gradually leaned, therebyperforming the air-fuel ratio control.

During such air-fuel ratio control, as shown in FIG. 2, if the enginemakes a transition from a non-idle state to an idle state (see FIG.2(A)) under the condition the engine speed Ne is equal to or greaterthan a predetermined speed Ne1 (see FIG. 2(E)), a target air-fuel ratiowill first be changed instantly to the third target air-fuel ratio AF2'and then a target air-fuel ratio for each control cycle will be set sothat it gradually approaches the second target air-fuel ratio AF2,thereby performing the air-fuel ratio control (see FIG. 2(B)).

On the other hand, along with this, a predetermined injection period αis set in accordance with the fuel injection mode at this time (here,the late lean mode in which fuel is injected on a compression stroke),and then whether or not the fuel injection period is less than thepredetermined injection period α is monitored (see a solid line C1 ofFIG. 2(C)). Then, with the aforementioned air-fuel control, the fuelinjection period is reduced quickly and smoothly, and if the fuelinjection period is less than the predetermined injection period α, thefuel cut mode will be selected and the fuel cut control will be switchedfrom an OFF state to an ON state, thereby executing the fuel cut (see asolid line D1 of FIG. 2(D)). In addition, after the transition from anon-idle state to an idle state (i.e., after the fuel cut conditionshave been established), a timer is started to count a period which ispresent after the transition to the idle state (here, it is counted as anumber of ignitions and the unit is referred to as "IG"). Even if thefuel injection period is not less than the predetermined injectionperiod α (see a chain line C2 of FIG. 2(C)), the fuel cut mode will beselected and fuel cut will be executed, if the second predeterminedperiod N2IG elapses after the fuel cut conditions have been established(see a chain line D2 of FIG. 2(D)).

Then, with such fuel cut, the engine speed Ne is gradually reduced. Ifthe engine speed is reduced to less than the predetermined speed (fuelinjection return condition speed) Ne2 even if the idle state continues(see FIG. 2(E)), then the magnitude |ΔNe| of the change rate ΔNe in theengine speed Ne at this time will be compared with a predetermined valueβ. If |ΔNe| is less than the predetermined value β (i.e., if a degree ofdeceleration is slight), a relatively lean return target air-fuel ratioB (=AF4) will be set. If |ΔNe| is equal to or greater than thepredetermined value β (i.e., if a degree of deceleration is great), arelatively rich return target air-fuel ratio (less than a stoichiometricair-fuel ratio) A (=AF3) will be set (see FIG. 2(B)). At the time of areturn to a fuel supply mode, fuel supply is started with these targetair-fuel ratios. Particularly, if the return target air-fuel ratio B(=AF4) is set, the target air-fuel ratio thereafter will be graduallyreduced toward the target air-fuel ratio A (=AF3) on a fuel-enrichedside.

Although the return target air-fuel ratio A (=AF3) has been set as thetarget air-fuel ratio for normal idle running, the return targetair-fuel ratio A may be set to a value lower than the target air-fuelratio for normal idle running (of course an air-fuel ratio higher thanthe return target air-fuel ratio B), and thereafter, the target air-fuelratio may be gradually reduced and returned to the target air-fuel ratiofor normal idle running. In other words, if a sudden increase in theoutput is performed when a degree of deceleration is great, the enginespeed will be returned, but a torque shock will easily occur. However,if a target air-fuel ratio is reduced stepwise in this manner, theengine speed can be returned avoiding a torque shock, as with thecontrol in the case of a small degree of deceleration. Furthermore, suchan advantage is obtainable with relatively simple control logic. Thereturn target air-fuel ratio in this case needs be set to one which canreturn engine speed and also avoid a torque shock.

If a further description is made of the fuel injection modes, in themode setting in the fuel injection modes, an enrich operating mode, astoichiometric operating mode, an early lean mode, and a late lean modeare generally set with respect to the engine speed Ne and the engineload Pe with an area tendency such as that shown in FIG. 6.

Also, among the aforementioned fuel injection modes, the late lean modecan realize the leanest combustion (air-fuel ratio: approximately 30through 40), and in this mode, the fuel injection is performed at astage extremely close to an ignition period, like the later stage of acompression stroke. Furthermore, fuel is collected near the spark plugto cause the air-fuel ratio to be rich partially and lean as a whole,whereby economical operation is performed ensuring ignitability andcombustion stability.

Then, the early lean mode can also realize lean combustion (air-fuelratio: approximately 20 through 24), and in this mode, the fuelinjection is performed at the intake stroke before the late lean mode.Fuel is diffused into the combustion chamber to cause the entireair-fuel ratio to be lean, and a certain degree of output is ensuredwhile ensuring ignitability, thereby performing economical operation.

The stoichiometric operating mode is made so that sufficient engineoutput is efficiently obtained, maintaining an air-fuel ratio at astoichiometric state or a state close to the stoichiometric state, basedon the output of the O₂ -sensor.

Also, in the open-loop combustion operating mode, combustion isperformed at an stoichiometric air-fuel ratio or an air-fuel ratioricher than this by open-loop control so that sufficient output isobtained at the time of acceleration or start.

First, if a description is made of the opening and closing controls ofthe valves 6 and 14, the ECU 16 is provided with a function of setting arequest air quantity in accordance with an engine operating state, andthe opening and closing controls of the valves 6 and 14 are performedaccording to the set request air quantity.

Specifically, as shown in FIG. 5, from the throttle opening degree θthdetected by the throttle sensor or the engine speed Ne based on both theoutput of the accelerator opening degree sensor (not shown) and thedetection information from the crank angle sensor, target engine load(target Pe) is first set based on the map (block B1).

If, on the other hand, the air conditioner is on, based on informationfrom the air-conditioner switch, an air-conditioner correspondingcorrection quantity Δ Peac will be set from the engine speed Ne, basedon the map (block B2). If the power steering wheel is on, based oninformation from the power steering wheel switch, a power steering wheelcorresponding correction quantity Δ Peps will be set from the enginespeed Ne, based on the map (block B3). Based on information from theinhibitor switch, an inhibitor corresponding correction quantity Δ Peinhwill be set from the engine speed Ne at the time of the start, based onthe map (block B4).

Then, with these corresponding correction quantities Δ Peac, Δ Peps, andΔ Peinh, the target Pe is corrected properly. Then, after thiscorrection the target Pe is filtered properly through the switch S1(block B5). From the thus obtained target Pe and engine speed Ne, acontrol quantity Pos for a valve opening degree corresponding to therequest air quantity (or a target intake-air quantity) Q is set based onthe map.

In setting this control quantity Pos, a map corresponding to an engineoperating state is selected from a plurality of maps shown in block B7and employed. Through switches S2 and S3, a signal is output inaccordance with an engine operating state. Here, as the engine operatingstate, maps are provided with respect to three modes: late lean mode inwhich the leanest combustion is carried out, early lean mode in whichthe second leanest combustion is carried out, and EGR in motion in astoichiometric operating mode. The request air quantity is set only inthe case of these modes.

Also, in the case where an idle operating state is established, thecontrol quantity #1ABVPos of the request air quantity (or targetintake-air quantity) #1ABVQ is set based on the feedback control ofengine speed by a switch S4, as shown in block B8. In this case thecontrol quantity #1ABVPos becomes a target opening degree based mainlyon the #1ABV valve.

The functional section for setting quantities corresponding to therequest air quantities Q and #1ABVQ through the aforementioned blocks B7and B8 corresponds to request air quantity setting means (not shown).

In accordance with the thus obtained control quantity Pos or #1ABVPos,the setting of the opening degree position of the air bypass valve 6 orthe setting of a duty ratio is performed (block B10) and the setting ofthe opening degree position of the air bypass valve 14 is performed(block B11), whereby the air bypass valves 6 and 14 are controlled atrequired states.

Furthermore, based on FIG. 5, a description will be made of each controlof the injector, the spark plug, and the EGR.

In order to drive the injector, there is a need to set the injectionstart period and injection end period of the injector, but, in thisembodiment, injector drive time Tinj and the injection end period of theinjector are set, and based on these, the timing for driving theinjector is determined calculating backward the injection start of theinjector. The settings of these are performed according to the operatingstate of the engine by the ECU 16.

In the setting of the injector drive time Tinj, an air-fuel ratio A/F isfirst set from the corrected target Pe and engine speed Ne given orobtained from the filtering process (block B6), based on the map (blockB12). Similarly, the setting maps in this case are provided with respectto four modes: EGR in motion in a late lean mode, EGR in stop in a latelean mode, early lean mode, and open-loop mode. The modes are selectedaccording to the operating state of the engine and employed.

From the thus obtained air-fuel ratio A/F and an intake-air quantity Qpbdetected by the air flow sensor, the injector drive time Tinj iscomputed (block B13).

Then, this injector drive time Tinj is given by-cylinders injectorunevenness rate correction (block B14) and by-cylinders dead timecorrection (block B15). On the other hand, from the target Pe and theengine speed Ne, injection time TDEC for deceleration is computed (blockB16). At the time of the deceleration of the engine and at the time ofthe late lean operating mode, a smaller time between the injector drivetime Tinj obtained in block B13 and the deceleration injection time TDECis selected through a switch S5 (block B17), and this is decided as theinjector drive time.

Similarly, in the setting of the injection end period of the injector,the injection end period is set from the corrected target Pe and enginespeed Ne given or obtained from the filtering process (block B6), basedon the map (block B18). The setting maps in this case are also providedwith respect to four modes: EGR in motion in a late lean mode, EGR instop in a late lean mode, early lean mode, and open-loop operating modeor stoichiometric feedback operating mode. The modes are selectedaccording to the operating state of the engine and employed.

In the case of the late lean mode, the thus obtained injection endperiod is given water temperature correction, thereby obtaining acorrected injection end period.

Based on the thus obtained injector drive time Tinj and injection endperiod, the injector is driven.

Also, for the ignition period of the spark plug by the spark coil, theignition period is set from the corrected target Pe and engine speed Negiven or obtained from the filtering process (block B6), based on themap (block B20). The setting maps in this case are provided with respectto five modes: EGR in motion in a late lean mode, EGR in stop in a latelean mode, early lean mode, EGR in motion in a stoichiometric feedbackoperating mode, and EGR in stop in an open-loop operating mode orstoichiometric feedback operating mode. The thus obtained ignitionperiod is given various retard corrections (block B21), and based onthis, control of the spark coil is performed.

Also, for the flow control of the EGR, the flow rate of the EGR is setfrom the corrected target Pe and engine speed Ne given or obtained formthe filtering process (block B6), based on the map (block B22). Thesetting maps in this case are provided with respect to four modes: latelean mode in a D range, late lean mode in an N range, stoichiometricfeedback operating mode in a D range, and stoichiometric feedbackoperating mode in an N range.

The thus obtained flow rate of the EGR is given water temperaturecorrection (block B23), and a control quantity (duty ratio)corresponding to an opening degree is set (block B24), therebyperforming the flow control of the EGR. Note that the water temperaturecorrection (block B23) also employs maps corresponding to engineoperating states (here, two modes: late lean mode and stoichiometricfeedback operating mode).

Since the fuel control apparatus for an in-cylinder injection internalcombustion engine as the first embodiment of the present invention isconstructed as described above, the fuel control is performed, forexample, as shown in FIG. 3.

In other words, initially the judgment means 103 judges whether or notthe engine is in deceleration (step S10). If it is in deceleration, thenthe judgment means 103 judges whether or not the fuel cut conditionshave been established, i.e., whether or not the engine is in an idlestate, from whether or not the idle switch is on (step S20). If it is ina non-idle state, the first target air-fuel ratio will be set so that itis gradually leaned according to the deceleration state from theair-fuel ratio corresponding to the operating state, and a targetair-fuel ratio for each control cycle will be set so that it graduallyapproaches this first target air-fuel ratio AF1, thereby controlling thefuel supply (step S170). In this manner, the output torque of the engineis reduced.

At the time of such target air-fuel ratio control, as shown in FIG. 2,if the engine makes a transition from a non-idle state to an idle state(see FIG. 2(A)) under the condition the engine speed Ne is equal to orgreater than a predetermined speed Ne1 (see FIG. 2(E)), a targetair-fuel ratio will first be changed instantly to the third targetair-fuel ratio AF2' and then a target air-fuel ratio for each controlcycle will be set so that it gradually approaches the second targetair-fuel ratio AF2, thereby controlling the air-fuel ratio control (seeFIG. 2(B)).

In this manner, even if the engine is in a non-idle state at the time ofdeceleration, the output torque of the engine will be reduced, andthereafter, in the case where the engine makes a transition to an idlestate (therefore, in the case where fuel cut conditions areestablished), a transition to a fuel cut mode can be made without atorque shock, and since this reduction in the output torque by theincrease in the air-fuel ratio is not suddenly performed, there is nopossibility that the driver, etc., will have a feeling of physicaldisorder.

Also, if the engine goes to an idle state at the time of thedeceleration, step S20 will advance to step S30 and the second targetair-fuel ratio (i.e., an air-fuel ratio even higher than the firsttarget air-fuel ratio) AF2 will be set so that the output torque of theengine will be further reduced.

Then, at the time the engine has gone to an idle state during theacceleration of the engine, if an actual air-fuel ratio has not beenincreased to the third target air-fuel ratio AF2' on a richer side thanthe second target air-fuel ratio AF2, an air-fuel ratio will first beincreased instantly to this third target air-fuel ratio AF2' and then atarget air-fuel ratio for each control cycle will be set so that itgradually approaches the second target air-fuel ratio AF2 even higherthan the third target air-fuel ratio, thereby performing control (stepS40).

Note that the third target air-fuel ratio AF2', by thus increasing anair-fuel ratio instantly at the time the engine has gone to an idlestate, causes a feeling of deceleration but does not cause a feeling ofshock (physical disorder). Also, if the target air-fuel ratio is thusset, the output torque of the engine can be sufficiently reduced and atransition to a fuel cut mode thereafter can be quickly performedwithout a torque shock. Since such a reduction in the output torque bythe increase in the air-fuel ratio is not suddenly performed, there isno possibility that the driver, etc., will have a feeling of physicaldisorder.

For such setting of the third target air-fuel ratio AF2', if a degree ofdeceleration is great, a torque shock will be in a direction where it isdifficult to occur, even if an air-fuel ratio is leaned, and therefore,a relatively great air-fuel ratio can be set to the third targetair-fuel ratio AF2'. According to the third target air-fuel ratio AF2'such as this, if the arrival time to the second target air-fuel ratioAF2 is shortened by leaning an air-fuel ratio, a reduction in fuelconsumption can be even further enhanced without deterioratingcombustion.

Then, it is judged whether or not all fuel cut conditions have beenestablished (step S50). This judgment is performed based on the resultof a judgment process such as that shown in a flowchart of FIG. 7. Asshown in the figure, it is first judged whether or not a basic fuel cutcondition has been established (step A10). This basic fuel cut conditionis one where the engine is in deceleration and also in an idling state(idle switch SW is on), and corresponds to the aforementioned steps S10and S20 of FIG. 3.

If the basic fuel cut condition is established, the countdown by thetimer will be started (step A20). This count will be startedconcurrently when the aforementioned step S30 of FIG. 3 advances to stepS40 and a control of getting the target A/F close to the AF2 is stared.In this step A20 the initial value T0 of the timer count, set accordingto the second predetermined period N2IG, is subtracted with apredetermined countdown unit.

Next, the setting means 104 sets the aforementioned predeterminedinjection period α in accordance with the operating mode at this time(fuel injection mode) (step A30).

Then, in step A40 it is judged whether or not the value of the timer(countdown value of the timer) has reached a predetermined value T1(corresponding to the elapse of the first predetermined period N1IG). Ifthe value of the timer does not reach the predetermined value T1, stepsA20 through A40 will be repeated, and the predetermined injection periodα will be updated, confirming whether or not fuel cut conditions havebeen established. If the value of the timer has reached thepredetermined value T1, step A40 will advance to step A50 and it will bejudged whether or not the fuel injection period (injector pulse width)is less than the predetermined injection period α.

If the fuel injection period (injector pulse width) is less than thepredetermined injection period α, step A50 will advance to step A70 andit will be assumed that all fuel cut conditions have been established.Also, even if the fuel injection period (injector pulse width) is notless than the predetermined injection period α, it will be assumed thatall fuel cut conditions have been established (step A70), if the timervalue has reached 0 (if the second predetermined period N2IG elapses),by the judgment in step A60 of whether or not the timer value (countdownvalue of the timer) has reached 0 (corresponding to the elapse of thesecond predetermined period N2IG).

Based on the result of such a judgment process according to fuel cutconditions, the judgment in step S50 of FIG. 3 is performed, and in thisstep S50, if it is judged that all fuel cut conditions have beenestablished, the process will advance to step S60 and fuel cut will beexecuted.

At the time of this fuel cut, initially the magnitude |ΔNe| of a changerate ΔNe in the engine speed Ne is compared with a predetermined value βand judged (step S70). If this |ΔNe| is less than the predeterminedvalue β (i.e., if a degree of deceleration is slight), a relatively leansecond return target air-fuel ratio (less than a stoichiometric air-fuelratio) B (=AF4) will be set (step S90). If |ΔNe| is equal to or greaterthan the predetermined value β (i.e., if a degree of deceleration isgreat), a relatively rich return target air-fuel ratio (less than astoichiometric air-fuel ratio) A (=AF3) will be set (step S80).

Subsequently, it is judged whether or not fuel supply return conditionshave been established (on the assumption that an idle state hascontinued) (step S100). Until the fuel supply return conditions areestablished, the return target air-fuel ratio B is properly varied bythe process of steps S60 through S90.

Then, if the fuel supply return conditions have been established, itwill be judged whether or not the target air-fuel ratio (A/F) of thecontrol cycle is less than A (step S110). If the return target air-fuelratio is B, step S110 will advance to step S120 through an No route andfuel supply will be returned with the return target air-fuel ratio as B.Furthermore, a target air-fuel ratio is adjusted gradually toward a richside (enriched side) so that the return target air-fuel ratio approachesA (step S130).

If the return target air-fuel ratio is B, the target air-fuel ratio(A/F) will become less than A through such a process. If the returntarget air-fuel ratio is A, the target air-fuel ratio (A/F) will becomeless than A through such a process. Thereafter, with the target air-fuelratio (A/F) as A, the process waits for a return from an idle state to anon-idle state and it is judged whether or not the engine is in anon-idle state (step S150). Then, if the engine is in a non-idle state,the engine will be returned to a normal operation (an operationindependent of fuel cut) and a target air-fuel ratio corresponding to anoperating state will be set, thereby performing operation (step S160).

In this manner, in this apparatus, both at the time of a transition to afuel cut mode and at the time of a return from a fuel cut mode to a fuelsupply mode, engine torque is adjusted by air-fuel ratio control.Therefore, the switching between a fuel cut mode and a fuel injectionmode can be performed without causing a torque shock. At the same time,since the fuel cut control is performed after the fuel injection period(injector pulse width) has been less than this predetermined injectionperiod α, a transition to a fuel cut mode is made after the torqueproduced by the engine has been reduced to some degree. Therefore, atransition to a fuel cut mode can be made, suppressing a torque shock atthe time of the transition to a fuel cut mode. Furthermore, in the casewhere the fuel injection period (injector pulse width) will not easilybecome less than the predetermined injection period α, the fuel cutcontrol is performed at the time the second predetermined period N2IGhas elapsed. Therefore, in this case, suppression of a torque shockcannot be sufficiently performed when a transition to a fuel cut mode ismade, but, since the injector pulse width has been less than the pulsewidth of the first predetermined period N1IG, a certain degree of shockcan be reduced and fuel cut effects, i.e., a fuel consumption savingeffect and an engine brake effect are obtainable with reliability.

Now, a second embodiment will be described in reference to FIG. 8.

As shown in FIG. 8, this embodiment is different in the controlimmediately before a transition to the fuel cut mode from the firstembodiment. In other words, in this embodiment, if the engine isdecelerated during non-idling, as with the first embodiment, the firsttarget air-fuel ratio (i.e., a high air-fuel ratio) AF1 will be set sothat the output torque of the engine is reduced. The target air-fuelratio for each control cycle is set so that it gradually approaches thefirst target air-fuel ratio AF1, and the fuel supply is controlled.However, thereafter, if the engine goes to an idle state duringdeceleration, the operating mode (fuel injection mode) will switchedfrom the compression stroke injection mode (late lean mode) to theintake stroke injection mode (stoichiometric mode or early lean mode).

If the operating mode is thus switched to the intake stroke injectionmode, the output torque of the engine will easily be reduced becauseirregular combustion which did not take place in the compression strokeinjection mode takes place in the engine. Therefore, as with MPIengines, a torque shock can be reduced when a transition to a fuel cutmode is made. In other words, if switching is performed from thecompression stroke injection mode to the intake stroke injection mode,the output torque of the engine will be reduced, because irregularcombustion will take place even if an increasing tendency is seen in thetorque output of the engine, as shown in FIG. 8(C). The fuel injectionperiod becomes less than a predetermined injection period α2 for theintake stroke injection mode (α2>α1, α: predetermined injection periodfor the compression stroke injection mode), whereby a torque shock canbe reduced when a transition to a fuel cut mode is made.

Thus, the second embodiment is capable of avoiding an uncomfortabletorque shock when a transition to a fuel cut mode is made, by switchingthe operating mode (fuel injection mode) from the compression strokeinjection mode to the intake stroke injection mode.

Note that the predetermined injection period α is set according to theoperating mode (fuel injection mode) of the engine. In the compressionstroke injection mode in which boost pressure is low and engine outputtorque is small, such as a late lean mode, the predetermined injectionperiod α is set relatively small. Therefore, there is another advantagethat a fuel cut effect is also obtainable, obtaining sufficiently thesuppression effect of torque shock occurrence.

In the intake stroke injection mode in which boost pressure is high andengine output torque is great, such as an early lean mode or astoichiometric mode, since the predetermined injection period α is setrelatively great, a suppression effect of torque shock occurrence and afuel cut effect can be balanced with each other.

Note that in this embodiment, while the first predetermined period N1IGhas been set and also the judgment means 103 has judged that fuel cutconditions have been established and confirmed that the throttle valvehas been fully closed after the elapse of the first predetermined periodN1IG, the apparatus of the present invention may omit the judgmentrelated to the first predetermined period N1IG, because the start offuel cut has been judged based on whether or not the fuel injectionperiod (injector pulse width) has been less than the predeterminedinjection period α and, in the case where the fuel injection period(injector pulse width) has been less than the predetermined injectionperiod α, it can be judged that the throttle valve has also been closedfully.

In addition, the predetermined injection period α has been taken to be afixed value in each operating mode, but, if it is varied according toengine speed or a degree of deceleration, control will be complicatedbut even finer control will be possible.

Industrial Applicability

According to the fuel control apparatus for an in-cylinder injectioninternal combustion engine of the present invention, a quick transitionto a fuel cut mode can be made suppressing a torque shock, andsimilarly, when fuel cut is returned to fuel supply, a return to fuelsupply can be performed suppressing a torque shock. Accordingly, thefuel control apparatus of the present invention can more efficientlyobtain advantageous effects, such as saving of fuel consumption by fuelcut and prevention of the excessive temperature rise of an exhaust gaspurifying catalyzer due to excess hydrocarbon (HC). If the fuel controlapparatus is applied, for example, to the engine of a vehicle such as anautomobile, it can simultaneously meet various demands for vehicleengines, such as operating cost reduction by low fuel consumption andenvironmental protection by acceleration of exhaust gas purification,enhancing drivability, and therefore it is extremely serviceable.

We claim:
 1. A fuel control apparatus for an in-cylinder injectioninternal combustion engine,the internal combustion engine injecting fueldirectly into a combustion chamber and also being able to selectaccording to an operating state of said internal combustion engine acompression stroke injection mode in which fuel injection is performedprimarily on a compression stroke, the fuel control apparatuscomprising: deceleration state detection means for detecting whether ornot said internal combustion engine is in a deceleration state; idledetection means for detecting whether or not said internal combustionengine is in an idle state; target air-fuel ratio setting means forsetting a target air-fuel ratio for said compression stroke injectionmode; and air-fuel ratio control means which can control an air-fuelratio, based on the target air-fuel ratio set by said target air-fuelratio setting means; wherein said target air-fuel ratio setting meanssets a first target air-fuel ratio as said target air-fuel ratio, whensaid deceleration state detection means detects that said internalcombustion engine is in a deceleration state and also said idle statedetection means detects that said internal combustion engine is not inan idle state, at the time of said compression stroke injection mode,and also sets as said target air-fuel ratio a value changed stepwisetoward a second target air-fuel ratio on a leaner side than said firsttarget air-fuel ratio, when said deceleration state detection meansdetects that said internal combustion engine is in a deceleration stateand also said idle detection means detects that said internal combustionengine is in an idle state, at the time of said compression strokeinjection mode.
 2. The fuel control apparatus for an in-cylinderinjection internal combustion engine as set forth in claim 1, whereinsaid first target air-fuel ratio is set so as to change stepwise to alean side.
 3. The fuel control apparatus for an in-cylinder injectioninternal combustion engine as set forth in claim 1, wherein said targetair-fuel ratio setting means first increases said target air-fuel ratioinstantly to a third target air-fuel ratio on a richer side than saidsecond target air-fuel ratio and then sets a value changed stepwisetoward said second target air-fuel ratio, when said deceleration statedetection means detects that said internal combustion engine is in adeceleration state and also said idle detection means detects that saidinternal combustion engine is in an idle state, at the time of saidcompression stroke injection mode.
 4. A fuel control apparatus for anin-cylinder injection internal combustion engine,the internal combustionengine injecting fuel directly into a combustion chamber and also beingable to select according to an operating state of said internalcombustion engine a fuel supply mode including a compression strokeinjection mode in which fuel injection is performed primarily on acompression stroke and a fuel cut mode in which supply of fuel to thecombustion chamber is cut, and furthermore being able to select saidcompression stroke injection mode when said fuel cut mode is returned tosaid fuel supply mode, the fuel control apparatus comprising:idledetection means for detecting whether or not said internal combustionengine is in an idle state; judgment means for judging whether or notreturn conditions from said fuel cut mode to said fuel supply mode havebeen established, based on detection information, from said idledetection means and the operating state of said internal combustionengine; deceleration state detection means for detecting a degree ofdeceleration of said internal combustion engine; target air-fuel ratiosetting means for setting a target air-fuel ratio for said compressionstroke injection mode; and air-fuel ratio control means which cancontrol an air-fuel ratio, based on the target air-fuel ratio set bysaid target air-fuel ratio setting means; wherein said target air-fuelratio setting means sets a first target air-fuel ratio as said targetair-fuel ratio, when said judgment means judges that said returnconditions have been established and also said degree of decelerationdetected by said deceleration state detection means is equal to orgreater than a predetermined value; also sets as said target air-fuelratio a second target air-fuel ratio on a leaner side than said firsttarget air-fuel ratio, when said judgment means judges that said returnconditions have been established and also said degree of decelerationdetected by said deceleration state detection means is less than thepredetermined value; and furthermore performs a return from said fuelcut mode to said fuel supply mode, while said air-fuel ratio controlmeans is controlling an air-fuel ratio with said first or second returntarget air-fuel ratio set by said target air-fuel ratio setting means,at the time of the establishment of said return conditions.
 5. The fuelcontrol apparatus for an in-cylinder injection internal combustionengine as set forth in claim 4, wherein said target air-fuel ratiosetting means is set so that in the case where said second return targetair-fuel ratio is set as said target air-fuel ratio, thereafter saidtarget air-fuel ratio is gradually reduced toward said first returntarget air-fuel ratio on a fuel-enriched side.
 6. The fuel controlapparatus for an in-cylinder injection internal combustion engine as setforth in claim 4, wherein fuel cut conditions for selecting said fuelcut mode are that rotation speed of said internal combustion engine isequal to or greater than a predetermined rotation speed and that saidinternal combustion engine is in an idle state.
 7. A fuel controlapparatus for an in-cylinder injection internal combustion engine,theinternal combustion engine injecting fuel directly into a combustionchamber and being able to select according to an operating state of saidinternal combustion engine a fuel supply mode including a compressionstroke injection mode in which fuel injection is performed primarily ona compression stroke an intake stroke injection mode in which fuelinjection is performed primarily on an intake stroke, and a fuel cutmode in which supply of fuel to the combustion chamber is cut, the fuelcontrol apparatus comprising:deceleration state detection means fordetecting whether or not said internal combustion engine is in adeceleration state; idle detection means for detecting whether or notsaid internal combustion engine is in an idle state; target air-fuelratio setting means for setting a target air-fuel ratio for saidcompression stroke injection mode; and air-fuel ratio control meanswhich can control an air-fuel ratio, based on the target air-fuel ratioset by said target air-fuel ratio setting means; wherein said targetair-fuel ratio setting means sets a first target air-fuel ratio as saidtarget air-fuel ratio, when said deceleration state detection meansdetects that said internal combustion engine is in a deceleration stateand also said idle detection means detects that said internal combustionengine is not in an idle state, at the time of said compression strokeinjection mode; and wherein said fuel supply mode is switched from saidcompression stroke injection mode to said intake stroke injection mode,when said deceleration state detection means detects that said internalcombustion engine is in a deceleration state and also said idledetection means detects that said internal combustion engine is in anidle state, at the time of said compression stroke injection mode. 8.The fuel control apparatus for an in-cylinder injection internalcombustion engine as set forth in claim 7, wherein fuel cut conditionsfor selecting said fuel cut mode are that rotation speed of saidinternal combustion engine is equal to or greater than a predeterminedrotation speed and that said internal combustion engine is in an idlestate.
 9. A fuel control apparatus for an in-cylinder injection internalcombustion engine,the internal combustion engine injecting fuel directlyinto a combustion chamber and also having a fuel cut mode in whichsupply of fuel to the combustion chamber is cut, and furthermore beingable to select said fuel cut mode in accordance with an operating stateof said internal combustion engine, the fuel control apparatuscomprising:injection period setting means for setting a fuel injectionperiod for said fuel injection valve; judgment means for judging whetheror not fuel cut conditions have been established, based on the operatingstate of said internal combustion engine; and mode selection means forselecting said fuel cut mode, if said judgment means judges that saidfuel cut conditions have been established and also the fuel injectionperiod set by said injection period setting means is less than apredetermined injection period.
 10. The fuel control apparatus for anin-cylinder injection internal combustion engine as set forth in claim9, wherein said mode selection means is constructed so that it selectssaid fuel cut mode, if said judgment means judges that said fuel cutconditions have been established but a state, in which the fuelinjection period set by said injection period setting means is not lessthan a predetermined injection period, continues only for apredetermined period.
 11. The fuel control apparatus for an in-cylinderinjection internal combustion engine as set forth in claim 9,whereinsaid in-cylinder injection internal combustion engine is provided with afuel injection mode including an intake stroke injection mode in whichfuel injection is performed primarily on an intake stroke and acompression stroke injection mode in which fuel injection is performedprimarily on a compression stroke, and is constructed so that these fuelinjection modes can be switched in accordance with the operating stateof said internal combustion engine; and wherein said predeterminedinjection period is set separately for each of said fuel injection modesand said predetermined injection period in said compression strokeinjection mode is set to a shorter period than said predeterminedinjection period in said intake stroke injection mode.
 12. The fuelcontrol apparatus for an in-cylinder injection internal combustionengine as set forth in claim 9, wherein fuel cut conditions forselecting said fuel cut mode are that rotation speed of said internalcombustion engine is equal to or greater than a predetermined rotationspeed and that said internal combustion engine is in an idle state.